Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	IPO	Convertible Preferred Stock	Common Stock	Common Stock IPO	Additional Paid-in Capital	Additional Paid-in Capital IPO	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ (142,542)			$ 1		$ 1,558		$ 26	$ (144,127)
Beginning balance (in shares) at Dec. 31, 2019			106,890,000
Beginning balance at Dec. 31, 2019			$ 417,359
Beginning balance (in shares) at Dec. 31, 2019				10,003,000
Vesting of restricted stock (in shares)				1,427,000
Exercise of stock options	2					2
Exercise of stock options (in shares)				2,000
Stock-based compensation expense	755					755
Unrealized gain (loss) on marketable securities, net	(10)							(10)
Net income (loss)	(32,875)								(32,875)
Ending balance at Mar. 31, 2020	(174,670)			$ 1		2,315		16	(177,002)
Ending balance (in shares) at Mar. 31, 2020			106,890,000
Ending balance at Mar. 31, 2020			$ 417,359
Ending balance (in shares) at Mar. 31, 2020				11,432,000
Beginning balance at Dec. 31, 2019	(142,542)			$ 1		1,558		26	(144,127)
Beginning balance (in shares) at Dec. 31, 2019			106,890,000
Beginning balance at Dec. 31, 2019			$ 417,359
Beginning balance (in shares) at Dec. 31, 2019				10,003,000
Net income (loss)	(172,135)
Ending balance at Sep. 30, 2020	(311,175)			$ 1		5,031		55	(316,262)
Ending balance (in shares) at Sep. 30, 2020			134,113,000
Ending balance at Sep. 30, 2020			$ 852,897
Ending balance (in shares) at Sep. 30, 2020				14,250,000
Beginning balance at Mar. 31, 2020	(174,670)			$ 1		2,315		16	(177,002)
Beginning balance (in shares) at Mar. 31, 2020			106,890,000
Beginning balance at Mar. 31, 2020			$ 417,359
Beginning balance (in shares) at Mar. 31, 2020				11,432,000
Issuance of Series B convertible preferred stock, net of issuance costs			$ 435,538
Issuance of Series B convertible preferred stock, net of issuance costs, (in shares)			27,223,000
Issuance of common stock in connection with license agreement	388					388
Issuance of common stock in connection with license agreement (in shares)				63,000
Vesting of restricted stock (in shares)				1,382,000
Exercise of stock options	35					35
Exercise of stock options (in shares)				24,000
Stock-based compensation expense	1,116					1,116
Unrealized gain (loss) on marketable securities, net	7							7
Net income (loss)	(87,808)								(87,808)
Ending balance at Jun. 30, 2020	(260,932)			$ 1		3,854		23	(264,810)
Ending balance (in shares) at Jun. 30, 2020			134,113,000
Ending balance at Jun. 30, 2020			$ 852,897
Ending balance (in shares) at Jun. 30, 2020				12,901,000
Vesting of restricted stock (in shares)				1,343,000
Exercise of stock options	9					9
Exercise of stock options (in shares)				6,000
Stock-based compensation expense	1,168					1,168
Unrealized gain (loss) on marketable securities, net	32							32
Net income (loss)	(51,452)								(51,452)
Ending balance at Sep. 30, 2020	(311,175)			$ 1		5,031		55	(316,262)
Ending balance (in shares) at Sep. 30, 2020			134,113,000
Ending balance at Sep. 30, 2020			$ 852,897
Ending balance (in shares) at Sep. 30, 2020				14,250,000
Beginning balance at Dec. 31, 2020	$ (421,184)			$ 2		8,216		30	(429,432)
Beginning balance (in shares) at Dec. 31, 2020	134,113,000		134,113,000
Beginning balance at Dec. 31, 2020	$ 852,897		$ 852,897
Beginning balance (in shares) at Dec. 31, 2020	16,170,000			16,170,000
Conversion of convertible preferred stock into common stock upon initial public offering	$ 852,897			$ 13		852,884
Conversion of convertible preferred stock into common stock, upon initial public offering (in shares)			(134,113,000)
Conversion of convertible preferred stock into common stock, upon initial public offering			$ (852,897)
Conversion of convertible preferred stock into common stock, upon initial public offering (in shares)				134,113,000
Issuance of common stock in initial public offering, net of offering costs		$ 626,405			$ 3		$ 626,402
Issuance of common stock in initial public offering, net of offering costs (in shares)					27,025,000
Vesting of restricted stock (in shares)				1,428,000
Exercise of stock options	298					298
Exercise of stock options (in shares)				205,000
Stock-based compensation expense	4,158					4,158
Unrealized gain (loss) on marketable securities, net	26							26
Net income (loss)	(180,617)								(180,617)
Ending balance at Mar. 31, 2021	881,983			$ 18		1,491,958		56	(610,049)
Ending balance (in shares) at Mar. 31, 2021				178,941,000
Beginning balance at Dec. 31, 2020	$ (421,184)			$ 2		8,216		30	(429,432)
Beginning balance (in shares) at Dec. 31, 2020	134,113,000		134,113,000
Beginning balance at Dec. 31, 2020	$ 852,897		$ 852,897
Beginning balance (in shares) at Dec. 31, 2020	16,170,000			16,170,000
Exercise of stock options (in shares)	1,121,000
Net income (loss)	$ (245,197)
Ending balance at Sep. 30, 2021	$ 830,085			$ 18		1,504,778		(82)	(674,629)
Ending balance (in shares) at Sep. 30, 2021	0		0
Ending balance (in shares) at Sep. 30, 2021	182,908,000			182,908,000
Beginning balance at Mar. 31, 2021	$ 881,983			$ 18		1,491,958		56	(610,049)
Beginning balance (in shares) at Mar. 31, 2021				178,941,000
Vesting of restricted stock (in shares)				1,423,000
Exercise of stock options	333					333
Exercise of stock options (in shares)				212,000
Stock-based compensation expense	4,941					4,941
Unrealized gain (loss) on marketable securities, net	(43)							(43)
Net income (loss)	18,683								18,683
Ending balance at Jun. 30, 2021	905,897			$ 18		1,497,232		13	(591,366)
Ending balance (in shares) at Jun. 30, 2021				180,576,000
Vesting of restricted stock (in shares)				1,628,000
Exercise of stock options	1,596					1,596
Exercise of stock options (in shares)				704,000
Stock-based compensation expense	5,950					5,950
Unrealized gain (loss) on marketable securities, net	(95)							(95)
Net income (loss)	(83,263)								(83,263)
Ending balance at Sep. 30, 2021	$ 830,085			$ 18		$ 1,504,778		$ (82)	$ (674,629)
Ending balance (in shares) at Sep. 30, 2021	0		0
Ending balance (in shares) at Sep. 30, 2021	182,908,000			182,908,000